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The University of Michigan plans to triple the number of study vehicles outfitted with vehicle-to-vehicle communications, the next phase of a road test of equipment designed to prevent accidents.

The school's Transportation Research Institute is expanding the 18-month test that already has involved nearly 3,000 cars, trucks, motorcycles and bicycles in the northeast part of Ann Arbor.

Phase 2 will be conducted during the next two years throughout the city with a fleet of 9,000 vehicles. This time, some pedestrians also will be given transmitters to see whether vehicles can spot their locations.

In a phone interview with Automotive News, James Sayer, a research scientist at the institute, said the communications system has worked well so far. For example, vehicles were able to pick up signals from traffic lights and other vehicles at a greater distance than expected.

That suggests that fewer roadside transmitters would be needed, which would reduce costs if the system is adopted for real-world use, Sayer said.

However, it is not yet known whether the cars and trucks equipped with communications devices had a lower accident rate.

In theory, vehicle-to-vehicle communications could help prevent rear-end crashes, accidents caused by lane changes and intersection crashes. Researchers are studying the data to assess the safety impact, Sayer noted.

The road test, which the university is conducting for the U.S. Department of Transportation, is expected to help federal regulators determine whether all vehicles should be equipped with transponders to transmit their location to any nearby car or truck.

The vehicles emit signals 10 times per second via a short-range communications channel similar to Wi-Fi. They have a range of 900 feet.

Although researchers still are poring over data gleaned from Phase 1, regulators and automakers have been cautiously upbeat.

On Feb. 3, the National Highway Traffic Safety Administration issued a statement that it will begin taking steps to enable vehicle-to-vehicle communication technology.

"By helping drivers avoid crashes, this technology will play a key role in improving the way people get where they need to go," said U.S. Transportation Secretary Anthony Foxx.

Meanwhile, automakers and suppliers view vehicle-to-vehicle communications as a key technology for autonomous vehicles. A Chicago supplier of navigation maps called Here is preparing to introduce detailed road maps that are accurate within a few centimeters.

Such maps could make use of vehicle-to-vehicle data to help an autonomous vehicle's computer anticipate potential hazards.